APD Carburetors make thier Maxspeed carburetors with an integral throttle stop built in and they have no restriction. They are a bit pricey though.
Gary at #1 Stops makes an excellent product(s) that work well.
I would talk to him about an air (Co2) operated stop that allows you to control the opening rate which reduces wheel spin when the stop comes off.
Tell him Billy Baer with the Midwest Super Comp Series sent ya.
Number 1 Stop Products
Gary Heuer
8403 West Ridgeway Ave.
Cedar Falls, IA 50613
Phone: 319.277.5290
Fax: 319.277.5242
Web:
www.number1stop.com
Email:
number1stop@number1stop.com